Computer system including a device with a plurality of identifiers

ABSTRACT

A host computer is connected with a magnetic disk storage device by a SCSI bus. In the magnetic disk storage device, a plurality of partitions are set in a disk drive unit and have device identifiers (ID&#39;s) respectively allocated thereto as SCSI ID&#39;s=1, 2 and 3, which are supported by a disk controller. When the host computer has acquired the control of the SCSI bus through an arbitration and has selected, for example, the partition with the device identifier SCSI ID=1, the disk controller permits the host computer to access the partition in response to the selection. Since the partitions are different in attributes, properties etc., they seem to be magnetic disk storage devices that at separate from one another when viewed from the host computer. Thus, the single magnetic disk storage device can be managed as a plurality of storage devices of different nature.

This application is a continuation of application Ser. No. 08/031,880filed Mar. 16, 1993, now U.S. Pat. No. 5,634,111.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a computer system and external storagetherefor. In particular, the computer system is such that devices ornodes have peculiar device ID's (identifiers) and are connected with oneanother through an interface or network, such as SCSI, IPI (IntelligentPeripheral Interface) or Ethernet, for exchanging data, commands,messages etc.

2. Related Art

As stipulated in, for example, ANSI X3. 131--1986, "Small ComputerSystem Interface (SCSI)" issued by ANSI (American National StandardsInstitute), the peripheral devices of a prior-art computer system havepeculiar device ID's, respectively. The LBA (Logical Block Address)lengths of the devices, the types of the devices (such as a randomaccess device, a sequential access device, a rewritable device, and aread only device), etc. are fixed for the respective devices bystandards. In addition, although not standardized, management for thedata reliabilities of the individual peripheral devices, management forbacking up the devices, etc. are carried out for the respective devicesat the request of the OS (operating system) of a host computer.

The prior-art technique is incapable of or has difficulty coping with acase, for example, where a magnetic disk storage device of largecapacity is divided into a plurality of partitions with the intention ofmanaging the partitions as separate storage areas of different nature(in points of the LBA lengths, the backup management, etc.).Accordingly, expensive and large-sized magnetic disk storage devicesneed to be installed for respective sorts of data of differentproperties, such as ordinary file data and image data.

Besides, it is not considered to share the peripheral devices between aplurality of hosts. The exclusive control between the hosts in the caseof a shared magnetic disk storage device cannot be performed on thedevice side, and is inevitably entrusted to the management of the hostside. For this reason, it is possible that some operations of the userof the computer system may bring about a situation where data held inthe magnetic disk storage device are destroyed.

Further, in case of a network including therein a node which isphysically connected in the same network, but which uses a communicationprotocol differing from that of the other nodes, it is difficult forsuch a single node to use two communication protocols properly and sohas difficulty communicating with the other nodes. Therefore, expensiveand large-sized magnetic disk storage devices must be installed for therespective different communication protocols.

SUMMARY OF THE INVENTION

The first object of the present invention is to solve the problems asstated above, and to provide a computer system which is permitted tohandle data of different properties by the use of an identicalperipheral device, and also an external storage device which serves asthe peripheral device.

The second object of the present invention is to provide a computersystem which is permitted to share a peripheral device among a pluralityof computers.

The third object of the present invention is to provide a computersystem which is permitted to share a peripheral device between computersof different communication protocols.

In order to accomplish the first object, the computer system accordingto the present invention is so constructed that peculiar device ID's(identifiers) are respectively allocated to a computer and theperipheral device, and that a plurality of device ID's are allocated tothe peripheral device.

Also, in order to accomplish the first object, the external storagedevice according to the present invention is so constructed that aplurality of partitions are set therein, and that device ID's areallocated to the respective partitions.

In order to accomplish the second object, the computer system accordingto the present invention is so constructed that peculiar device ID's arerespectively allocated to the plurality of computers and peripheraldevices, and that a plurality of device ID's are allocated to thespecified peripheral device.

In order to accomplish the third object, the computer system accordingto the present invention is so constructed that device ID's areallocated to the respective computers, and that device ID's differingfor the respective communication protocols are allocated to theperipheral device.

In accordance with the first-mentioned construction of the presentinvention, when the computer has selected the peripheral device bydesignating any of the plurality of device ID's allocated to theperipheral device, this peripheral device responds to the computer, andthe computer can access the peripheral device in regard to thedesignated device ID. Accordingly, the peripheral device seems to thecomputer to be a number of devices, in fact as many as the number ofallocated device ID's, and the computer can handle the data of thedifferent properties by the use of the peripheral device.

With the second-mentioned construction, the device ID's are respectivelyallocated to the partitions of the external storage device. Therefore,when the computer has selected the external storage device bydesignating one of the device ID's, it can access the partition havingthe designated device ID. Accordingly, the partitions form separatedevices when viewed from the computer, and the data with propertiesdiffering for the respective partitions can be written into and read outof these partitions.

With the third-mentioned construction, when the separate computers haveselected the specified peripheral device by designating the pertinentones of the plurality of allocated device ID's, they can access theperipheral device in regard to the designated device ID's. In this case,when the plurality of device ID's allocated to the single peripheraldevice are individually held in correspondence with the separatecomputers, the peripheral device becomes capable of performing theexclusive control between the computers. Moreover, when at least twocomputers are allowed to designate a predetermined one of the deviceID's, they can share the peripheral device by using this predetermineddevice ID.

With the fourth-mentioned construction, the device ID's for therespective communication protocols are allocated to the peripheraldevice. Therefore, no matter which communication protocol the computerhaving selected the peripheral device may have, the computer can accessthe peripheral device in regard to the device ID designated by thiscomputer. Accordingly, the plurality of computers having differentcommunication protocols can share such a peripheral device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of a computer systemaccording to the present invention;

FIG. 2 is a block diagram showing a practicable example of a magneticdisk storage device depicted in FIG. 1;

FIG. 3 is a block diagram showing another embodiment of the computersystem according to the present invention;

FIG. 4 is a block diagram showing still another embodiment of thecomputer system according to the present invention;

FIG. 5 is a block diagram showing yet another embodiment of the computersystem according to the present invention;

FIG. 6 is a block diagram showing a further embodiment of the computersystem according to the present invention; and

FIG. 7 is a block diagram showing the arrangement of the principalportions of a SCSI control LSI (large-scale integrated circuit) depictedin FIG. 2.

PREFERRED EMBODIMENTS OF THE INVENTION

Now, embodiments of the present invention will be described withreference to the drawings.

FIG. 1 is a block diagram illustrative of one embodiment of a computersystem according to the present invention. The computer system of thisembodiment comprises a host computer 1, a SCSI bus 2, and a magneticdisk storage device 3. The magnetic disk storage device 3 includes adisk drive unit 4 divided into partitions 41, 42 and 43, and a hard diskcontroller 5.

As illustrated in the figure, in this embodiment the host computer 1 andthe magnetic disk storage device 3, which serves as external storage forthe computer 1, are connected by the bus 2 conforming to the SCSI whichhas recently become the standard for peripheral equipment interfaces forsmall computer systems. The magnetic disk storage device 3 is configuredof the hard disk controller 5 and the disk drive unit 4.

Here, the prior art will be explained for the sake of comparison. In aprior-art computer system having such an architecture, the host computer1 and the magnetic disk storage 3 have respective device ID's(identifiers) such as SCSI ID=1 for the former and SCSI ID=2 for thelatter. The host computer 1 issues comands and exchanges commands,messages and data with the magnetic disk storage device 3 after an"arbitration phase" for acquiring the control of the bus 2 to be aninitiator and a "selection phase" for selecting the magnetic diskstorage device 3 which is the opposite party of the host computer 1. Byway of example, in a case where the host computer 1 is to read data outof the magnetic disk storage device 3, the arbitration phase is firstexecuted so that the host computer 1 may acquire the bus control of theSCSI bus 2 and occupy this bus 2. Subsequently, the selection phase isexecuted so that the magnetic disk storage device 3 may be designated asthe target device. On this occasion, the magnetic disk storage device 3knows that the host computer 1 is about to select the storage device 3itself, from the device ID sent by the host computer 1 (actually, atransmission line corresponding to the device ID is electricallydriven). Then, the magnetic disk storage device 3 responds to the deviceID, thereby informing the host computer 1 of the fact that the storagedevice 3 is ready to accept a command. The selection phase is completedby the response.

This embodiment is quite similar to the prior art in that the peculiardevice ID (here, SCSI ID=7) is set for the host computer 1, and that thehost computer 1 undergoes the arbitration and executes the selection.However, it differs from the prior art in that the opposite device,here, the magnetic disk storage device 3 has a plurality of device ID's.More specifically, as shown in FIG. 1, in the magnetic disk storagedevice 3, the disk drive unit 4 is divided into partitions, for example,the three partitions 41, 42 and 43, for which the different device ID's(here, SCSI ID's=1, 2 and 3) are respectively set. Thus, when viewedfrom the host computer 1, the magnetic disk storage device 3 seems to bethree separate magnetic disk storage devices connected to the SCSI bus2. Since three or more devices do not use one bus simultaneously inaccordance with the SCSI standards, one device can have a plurality ofdevice ID's allocated thereto and be made to look like a plurality ofdevices.

FIG. 2 is a block diagram showing a practicable example of the magneticdisk storage device 3 depicted in FIG. 1. This magnetic disk storagedevice 3 includes a SCSI control LSI (large-scale integrated circuit) 6which is configured of ID registers 71, 72, . . . and 73. It alsoincludes a disk control LSI 8, a buffer memory 9, CPU's 101 and 102, aPLL/ENDEC (phase-locked loop circuit/encode-decode circuit) 11, aread/write signal processing circuit 12, and a magneticrecording/reproducing head 13.

In the illustrated example, the disk controller 5 is configured of theSCSI control LSI 6, the disk control LSI 8, the CPU's 101 and 102 whichcontrol the respective LSI's 6 and 8 by the use of microprograms, andthe buffer memory 9 which is a data transferring buffer. In this regard,a SCSI control LSI included in a disk controller in the prior art isprovided with only one register for storing one device ID of its owntherein. In the selection phase, the SCSI control LSI in the prior artperforms a control in which a device ID requested by the host computeris compared with the device ID of its own stored in the register. Whenthe device ID's are coincident, the SCSI control LSI responds to therequest of the host computer and prepares for subsequently accepting acommand from the host computer, and when not, it does not respond.

In contrast, the SCSI control LSI 6 shown in FIG. 2 is provided with theplurality of ID registers 71, 72 and 73 in which the device ID's (here,SCSI ID's=1, 2 and 3) set for the partitions of the disk drive unit 4are respectively stored. In the selection phase executed by the hostcomputer 1, the SCSI control LSI 6 compares a device ID requested by thehost computer 1, with the device ID's stored in any of the ID registers71˜73. When the requested device ID coincides with any of the storeddevice ID's, the SCSI control LSI 6 acknowledges the coincidence andresponds to the request of the host computer 1. On this occasion, theSCSI control LSI 6 notifies the device ID requested by the host computer1, to the CPU 101 controlling this LSI 6, and it prepares forinterpreting a command to be subsequently sent from the host computer 1,in accordance with the called device ID. Likewise, the SCSI control LSI6 notifies the device ID requested by the host computer 1, to the diskcontrol LSI 8 and the CPU 102 controlling this LSI 8. The notificationis necessitated for instructing the disk drive 4 to execute anappropriate process or for appropriately controlling the buffer memory 9after having interpreted the command such as the conversion of an LBA(logical block address) into a PBA (physical block address).

In actual fact, the SCSI control LSI 6 need not be provided with theplurality of ID registers. In a case where the number of device ID's inthe whole system is limited to eight as in the SCSI standards, the SCSIcontrol LSI 6 may well be provided with one ID register of 8 bits, thestages of which are respectively held in correspondence with theseparate device ID's so as to store one device ID with one bit.

The protocol of the SCSI standards consists of the following sevenphases:

1) Arbitration Phase;

An initiator (a term in the SCSI standards, signifying a device on aside on which a command is issued) acquires the control of a SCSI bus.When a plurality of initiators have simultaneously intended to acquirethe bus control, the priority sequence of the initiators is determinedon the basis of the ID's thereof.

2) Selection Phase;

The initiator having acquired the bus mastership designates the ID of atarget (a term in the SCSI standards, signifying a device on a side onwhich a command is executed). The designation is done by making "true"that data line among eight data lines which corresponds to the ID No. ofthe target. The target recognizes that it has been selected.Thenceforth, it undergoes a phase transition until a bus free status isrestored at the end of the execution of the command.

3) Command Phase;

The initiator sends the command to the target.

4) Data Phase;

In the case of the command, such as read or write, which requires thetransfer of data, the target changes its phase from the command phase tothe data phase, and it awaits the data transfer from the initiator forthe write command or transfers the data to the initiator for the readcommand.

5) Status Phase;

The target reports the result of the command execution to the initiator.

6) Message Phase;

The target sends a message indicative of the completion of the commandto the initiator.

7) Bus Free Phase;

After sending the message, the target restores the SCSI bus to the busfree status which is an unused status.

FIG. 7 illustrates the arrangement of the principal portions of the SCSIcontrol LSI 6 in this embodiment.

This SCSI control LSI 6 includes comparators 74˜76 in correspondencewith the respective ID registers #˜#n (71, 72 and 73). The comparators74˜76 compare the ID No. asserted in the selection phase, with thecontents of the respective ID registers 71˜73. When the ID No. hascoincided with any of the contents, the SCSI control LSI 6 generates anID coincidence signal at the corresponding comparator. Then, the LSI 6informs the CPU 101 of the ID No. having coincided, in other words, thedevice ID requested by the host computer 1. The CPU 101 executes thesubsequent processing of the command, using mode information (parameterssuch as the logical block length of the device) set for every device ID.As a preferable example, the mode information is held in a nonvolatilememory, such as disk or ROM, during the turn-OFF of the power source ofthe computer system, whereas it is held in the working memory (notshown) of the CPU 101 during the operation of the computer system. Byway of example, the working memory is provided in the CPU chip 101, inthe disk control LSI 8, in the buffer memory 9, or in the SCSI controlLSI 6.

It is now assumed that the device identifier SCSI ID=1 has beenrequested by the host computer 1. In a case where a read command hasbeen subsequently sent from the host computer 1, the disk control LSI 8and CPU 102 of the disk controller 5 interpret the device ID (=1) of thedevice having responded in the selection phase, and an LBA designated inthe command by the host computer 1. Next, the disk controller 5 convertsthe LBA into a PBA which expresses a physical position in the disk drive4. Further, data are read out of the partition 41 of the disk drive 4 bythe use of the buffer memory 9 and the EN/DEC PLL 11 as well as theread/write signal processing circuit 12. In this embodiment, therecording area of a magnetic disk (not shown) is divided into thepartitions 41˜43, and the data are read out in a subarea correspondingto the partition 41 by the magnetic recording/reproducing head 13. Awrite command is executed similarly. A PBA is obtained from the deviceID of the device having responded in the selection phase, and an LBAdesignated in the command by the host computer 1. Data are written inthe partition corresponding to the PBA.

Here, in both the read and write operations, the single magnetic diskstorage device 3 is endowed with different attributes (concerning, forexample, an LBA length, the management of the buffer memory, and aprocessing method on the occurrence of an error) for the respectivepartitions 41, 42 and 43 which correspond to the device ID's (SCSIID's=1, 2 and 3) set in this storage device 3. In the prior art, such anattribute is set for every device by a mode select command and cannot bechanged for respective partitions. Since, as stated above, the differentattributes are afforded to the respective partitions, the LBA lengthsand the buffer memory management methods can be set so as to maximizeeffective transfer rates in accordance with the characteristics of datawhich are to be stored in the partitions. Besides, the buffer memorymanagement methods and the error processing methods can be set inaccordance with the required reliabilities of the data.

In the SCSI standards, the above expedient can be substituted byallocating different LUN's (logical unit numbers) to the respectivepartitions 41˜43.

As thus far described, in this embodiment, the single magnetic diskstorage device 3 seems to be three magnetic disk storage devices whenviewed from the host computer 1.

Thus, the partition 43 of the device identifier SCSI ID=3, for example,can be set as a partition for storing therein data created by the userof the computer system, only this partition being backed up at a fixedtime every day, and the partition 41 of the device identifier SCSI ID=1, for example, can be set as a partition for storing the OS (operatingsystem) of the computer system therein, whereby the logically separatepartitions are respectively managed with ease. Alternatively, thepartition 41 and the partition 42 of the device identifier SCSI ID=2,for example, can be respectively assigned as a file area for ordinaryfiles and as a file area for a real time control, or the partitions 41and 42, for example, can be respectively assigned as a file area forordinary files and as a file area dedicated to motion pictures, wherebythe block lengths, the architectures of file systems (such as directorymanagement systems), data protection attributes, etc. are optimized forthe respective partitions with ease.

FIG. 3 is a block diagram illustrative of another embodiment of thecomputer system according to the present invention. Numeral 14 indicatesa disk array storage device, which includes a disk array controller 15,a buffer memory 16, and a disk array 17 divided into partitions 171, 172and 173.

This embodiment employs the disk array storage device 14. In FIG. 3, thedisk array storage device 14 supports four SCSI identifiers (SCSIID's=0, 1, 2 and 3), which correspond respectively to the buffer memory16, partition 171, partition 172 and partition 173. As in the foregoingembodiment shown in FIG. 1, a host computer undergoes an arbitration andexecutes a selection. The disk array controller 15 judges which of thefour devices consisting of the buffer memory 16 and the three partitions171, 172 and 173 corresponds to a command or data sent via a SCSI bus 2from the host computer, on the basis of a device ID requested by thehost computer. Subsequently, it performs processing for thecorresponding device.

Although the four devices with the different device ID's, namely, thebuffer memory 16 and the partitions 171 173 are collectively managed bythe disk array controller 15, they are storage areas which havecharacteristics differing from one another. By way of example, thecharacteristics are as stated below. The buffer memory 16 is asemiconductor disk, the capacity of which is usually small, but whichexhibits a very high response rate. Besides, the partition 171 is"RAID(Redundant Arrays of Inexpensive Disks)1" which is a disk array ofmirror disk configuration. Since data are overwritten into the diskarray 171, the reliability thereof is very high. In addition, thepartition 172 is "RAID3" which is a disk array for high-speed datatransfer. The disk array 172 is suited to quick transfer of long datasuch as the data of a motion picture, or the data of a gigantic arraysuch as which would be handled in a scientific or technologicalcomputation. Further, the partition 173 is "RAID5" which is a disk arrayfor heavy transactions. The disk array 173 is suitable for anapplication, such as database or network server, in which a data lengthto be handled is comparatively short, but the number of I/O(input/output) processes per unit time is large. When viewed from thehost computer, all the four devices 16 and 171˜173 seem to beindependent of one another. As described in the preceding embodiment,therefore, the attributes of the individual devices 16 and 171˜173,concerning the block length, the buffer memory management, the errorprocessing method, the backup method, etc. can be optimized and set withease, and the disk array controller 15 can manage these attributes withease. To this end, which of the devices 16 and 171˜173 is to be accessedmay be judged on the basis of the device ID designated in the selectionphase by the host computer, so as to distribute a command process to thejudged device. The attributes of the respective devices, such as theblock lengths, may be held within the disk array controller 15 (forexample, in the internal register of the disk control LSI 8 or theregister of the CPU 102 as shown in FIG. 2) so as to be used ininterpreting the command of the host computer.

FIG. 4 is a block diagram illustrative of still another embodiment ofthe computer system according to the present invention. In FIG. 4,symbols 1A and 1B denote host computers, and portions corresponding tothose of the embodiment shown in FIG. 1 are denoted by the samenumerals.

The embodiment shown in FIG. 4 is such that a single magnetic diskstorage device 3 is shared by the plurality of host computers 1A and 1B.

Referring to FIG. 4, the magnetic disk storage device 3 is connected tothe two host computers 1A and 1B through a SCSI bus 2. It includes adisk controller 5, and a disk drive unit 4 in which three partitions 41,42 and 43 are set. Here in this embodiment, the partition 41 (SCSI ID=1)is assigned to the host computer 1A, the partition 42 (SCSI ID=2) isassigned to the host computer 1B, and the partition 43 (SCSI ID=3) isassigned to both the host computers 1A and 1B so as to be shared.

Even in the prior art, a single magnetic disk storage device issometimes shared by a plurality of host computers. In such a case,however, the exclusive control between the host computers must beresponsibly managed on the host computer side. Therefore, erroneousoperation by the user of a computer system might incur the problem of,e. g., data destruction arising in such a manner that, after data havebeen written into a certain area by one of the host computers, data arewritten into the same area by the other host computer.

On the other hand, in this embodiment, the host computer 1A is set bythe OS (operating system) of the computer system beforehand so as toaccess only the partitions 41 and 43 respectively having the SCSI ID's=1and 3, as stated above. Then, the host computer 1A can request only theSCSI ID's=1 and 3, and it is prevented from erroneously accessing thepartition 42 which is an area dedicated to the host computer 1B.Besides, the partition 43 is a read only area, and it is readily set soas to be shared by the host computers 1A and 1B. Although the partition43 can be accessed by both the host computers 1A and 1B, it undergoes nodata destruction since it is a read only area. Further, in a case wherethe disk controller 5 performs the exclusive control between an accessfrom the host computer 1A and an access from the host computer 1B, itneed not consider the difference of the device ID's (here, SCSI ID's=7and 6) of the respective host computers 1A and 1B, but it may merelyjudge the pertinent ones of the device ID's (SCSI ID's=1, 2 and 3) ofthe respective partitions 41, 42 and 43 selected by the host computers1A and 1B. Processing which is executed for interpreting a command bythe disk controller 5 is similar to that explained in conjunction withFIG. 2.

FIG. 5 is a block diagram illustrative of yet another embodiment of thecomputer system according to the present invention. In FIG. 5, numerals21 and 22 indicate SCSI buses, and numeral 18 indicates a printer.Portions corresponding to those of the embodiment shown in FIG. 4 aredenoted by the same numerals.

The computer system of this embodiment has such an architecture that aplurality of host computers are interconnected by a SCSI bus, and thatperipheral devices are connected to only one of the host computers byanother SCSI bus.

Referring to FIG. 5, host computers 1A and 1B are interconnected by theSCSI bus 21, and a magnetic disk storage device 3 and the printer 18 areconnected to the host computer 1B by the SCSI bus 22. Here, as in theembodiment shown in FIG. 4, the magnetic disk storage device 3 includesa disk controller 5 and a disk drive unit 4 divided into partitions 41,42 and 43 of respective SCSI ID's=1, 2 and 3. The device ID of theprinter 18 is set at SCSI ID=4. The host computer 1B supports the deviceID (SCSI ID=6) of its own, the device ID's (SCSI ID's=1, 2 and 3) of thepartitions 41, 42 and 43, and the device ID (SCSI ID=4) of the printer18, while the host computer 1A supports the device ID (SCSI ID=7) of itsown.

In the prior art, in a case where the host computer 1A is to access anyof the peripheral devices such as the magnetic disk storage device 3 andthe printer 18 which are located below the host computer 1B as statedabove, this host computer 1A undergoes an arbitration so as to acquirethe control of the SCSI bus 21. Thereafter, the host computer 1A selectsthe host computer 1B of the SCSI ID=6 and causes the host computer 1B torun a program (which is a program complying with the command of the hostcomputer 1A). Subsequently, the host computer 1A sends the host computer1B a command for designating the device ID of the magnetic disk storagedevice 3 or the printer 18 and the operation of the correspondingdevice, and the host computer 1B executes the command on the basis ofthe above program so as to access the designated device by the use ofthe device ID thereof. That is, in the case where the host computer 1Ais to access the predetermined device, the host computer 1B accesses thedevice instead. Therefore, the accesses from the host computer 1A to thedevices such as the magnetic disk storage device 3 and the printer 18are troublesome. Moreover, the dedicated program for operating the hostcomputer 1B as stated above needs to be installed in this host computer1B.

On the other hand, in this embodiment, the host computer 1B bears, notonly the SCSI ID=6 being the device ID of its own, but also the SCSIID=4 of the printer 18 and the SCSI ID's=1, 2 and 3 of the respectivepartitions 41, 42 and 43 of the magnetic disk storage device 3. When thehost computer 1A sends one of the device ID's, for example, the SCSIID=1 to the host computer 1B, the host computer 1B executes an operationequivalent to its operation responsive to the instruction of accessingthe partition 41 of the magnetic disk storage device 3, and it undergoesan arbitration for the SCSI bus 22 and selects the partition 41 as inthe preceding embodiment, thereby accessing this partition 41.

In this manner, according to this embodiment, the host computer 1A canaccess either of the magnetic disk storage device 3 and the printer 18,which are not directly connected thereto, equivalently through the hostcomputer 1B (namely, as if the host computer 1B were not existent)merely by sending the device ID of the device to-be-accessed directlywithout the necessity of calling the host computer 1B. It is alsopossible for the host computers 1A and 1B to share the single magneticdisk storage device 3 in the same manner as in the embodiment shown inFIG. 4. Of course, in this case, the host computer 1B must respond toany accesses to the devices of the SCSI ID's=1, 2, 3 and 4 on the SCSIbus 21 and then deliver a command or data from the host computer 1A tothe SCSI bus 22. Contrariwise, it must respond to an access to the hostcomputer 1A of the SCSI ID=7 on the SCSI bus 22 and then deliver acommand or data to the SCSI bus 21. Such requisites, however, are notobjectionable as explained below. In general, in a case where remoteprinting, file transfer or the like is to be executed via a network, acommand or data is interpreted tracing back to an application layer,whereupon an access to a printer, a magnetic disk storage device or thelike is controlled. In contrast, according to this embodiment, merelythe command of substantially the same content and in the same format maybe transferred, so that processing and labor are greatly simplified andsaved.

By the way, even when the SCSI bus 21 is replaced with a network such asEthernet in FIG. 5, the host computer 1A can access any of theperipheral devices such as the magnetic disk storage device 3 andprinter 18, which are not directly connected to this host computer 1Aphysically, equivalently through the host computer 1B. Also, the singlemagnetic disk storage device 3 can be shared by the host computers 1Aand 1B (while realizing the exclusive control which does not burden thehost computers) as in the embodiment shown in FIG. 4. In this case,however, the host computer 1B must accept and deliver commands and datain which the differences of communication protocols for the SCSI bus 21and Ethernet are considered.

FIG. 6 is a block diagram illustrative of a further embodiment of thecomputer system according to the present invention. The computer systemcomprises host computers 1A ˜1D, a network file server 19, and Ethernet22 as a network. The network file server 19 includes a network fileserver controller 20, and a magnetic disk storage device 21 which isdivided into partitions 211˜213.

This embodiment consists in that a plurality of host computers whichdiffer in, for example, communication protocols are connected by anetwork file server and a network.

Here in FIG. 6, the host computers 1A and 1B are MS-DOS (Microsoft DiskOperating System) machines, the IP (internet protocol) addresses ofwhich are respectively set at 3001 and 3002. The host computer 1C is ashared machine for UNIX and MS-DOS, and it is set at an IP address of1002 for UNIX and an IP address of 3003 for MS-DOS. The host computer 1Dis a shared machine for UNIX and the OS (operating system) of alarge-sized general-purpose computer, and it is set at an IP address of1001 for UNIX and an IP address of 5001 for the large-sizedgeneral-purpose computer. In addition, the network file servercontroller 20 supports IP addresses=1003, 3004 and 5002, whichcorrespond respectively to the partition 211 for UNIX, the partition 212for the large-sized general-purpose computer, and the partition 213 forMS-DOS in the magnetic disk storage 21. Besides, the host computers1A˜1D are connected to the network file server controller 20 throughEthernet 22 which is one example of the network.

In such an architecture, the host computers 1A˜1D have different OS'sand different network protocols (communication protocols), and thepartitions 211˜213 of the magnetic disk storage device 21 arerespectively held in correspondence with the OS's and network protocolswhich differ from one another. That is, the network file servercontroller 20 of the network file server 19 supports the IPaddresses=1003, 3004 and 5002 and controls the magnetic disk storagedevice 21 as follows: The partition 211 of the storage device 21 set asthe partition for UNIX can be accessed only with the OS and networkprotocol of UNIX. The partition 212 set as the partition for thelarge-sized general-purpose computer can be accessed only with thenetwork protocol of the OS for the large-sized general-purpose computer.The partition 213 set as the partition for MS-DOS can be accessed onlywith the network protocol of MS-DOS.

When the host computers 1C and 1D operate in conformity with UNIX, theycan request to the network file server controller 20 for the IPaddress=1003. Besides, when the host computer 1D operates in conformitywith the OS for the large-sized general-purpose computer, it cansimilarly request for the IP address=5002.

Owing to the control stated above, when the host computer 1C, forexample, is to access the magnetic disk storage device 21 of the networkfile server 19 in conformity with MS-DOS, it requests the network fileserver controller 20 to select the IP address=5002 through Ethernet 22.Then, the network file server controller 20 controls the magnetic diskstorage device 21 in order that the host computer 1C may be enabled toaccess the partition 213 of the magnetic disk storage device 21 with thenetwork protocol of MS-DOS.

In this manner, the identical network file server 19 can be easilyshared among the host computers which have the different networkprotocols and OS's.

Incidentally, when the host computers 1A and 1C are to communicate ortransfer data therebetween, the IP address for MS-DOS (=3003) set forthe host computer 1C is designated, whereby the network protocol forMS-DOS is automatically used between the computers 1A and 1C. In thecommunications or data transfer between the host computers 1C and 1D,the IP addresses for UNIX (=1002 and 1001) are respectively designatedfor these computers 1C and 1D, and the network protocol for UNIX isused. Thus, the different sorts of machines can be connected with ease.

As described above in detail, according to the present invention, aplurality of device ID's are allocated to each device, wherebypartitions corresponding to the respective device ID's can be endowedwith attributes differing from one another, and the attributes can beoptimized in accordance with the characteristics of data which are to behandled in the individual partitions.

In addition, an exclusive control, which is required in a case where asingle peripheral device is shared among a plurality of host computers,can be performed with ease, the destruction of data attributed to anerroneous operation can be prevented, and the settings of backupmanagements, etc. are facilitated.

Further, the control of accesses to partitions having differentperformances in, e. g., a disk array can be performed with ease.

Still further, part of a transfer buffer included in a disk controllercan be set as a semiconductor disk and accessed from a host computereasily without altering a protocol.

Yet further, a host computer can equivalently and easily access aperipheral device which is connected to only another host computer.

Moreover, even in case of a network file server, the single file servercan be easily shared among different sorts of machines which differ infile systems and network protocols, and accesses can be efficientlycontrolled in a network in which host computers supporting a pluralityof OS's and protocols are coexistent.

What is claimed is:
 1. A disk array storage device, comprising:a diskarray which is divided into a plurality of partitions; and a disk arraycontroller connectable to a host computer via a Small Computer SystemInterface (SCSI) bus and to said disk array; wherein said disk arraycontroller allocates a different SCSI-ID to each of said plurality ofpartitions, said disk array controller receives an SCSI-ID from the hostcomputer via said SCSI bus, said disk array controller recognizes if thereceived SCSI-ID coincides with any of the SCSI-IDs allocated to any ofsaid plurality of partitions, said disk array controller responds to thehost computer if coincidence is recognized, said disk array controllerreceives an SCSI command from the host computer, said disk arraycontroller selects one of said partitions corresponding to the SCSI-IDreceived from the host computer, and said disk array controller controlsaccess to the selected partition in accordance with the SCSI commandreceived from the host computer and transfers a result of the access tothe host computer.
 2. A disk array storage device according to claim 1,wherein the SCSI command includes a Logical Unit Number.
 3. A disk arraystorage device according to claim 1, wherein each of said partitionsincludes portions of multiple disks of said disk array.
 4. A disk arraystorage device according to claim 3, wherein each of said partitions isassigned one of RAID levels.
 5. A disk array storage device,comprising:a disk array divided into a plurality of partitions, eachassigned a different Small Computer System Interface (SCSI) ID; and adisk array controller connectable to a host computer via an SCSI bus andto said disk array; wherein said disk array controller receives anSCSI-ID from the host computer via said SCSI bus, recognizes if thereceived SCSI-ID coincides with any of the SCSI-IDs assigned to saidplurality of partitions, responds to the host computer if coincidence isrecognized, receives an SCSI command from the host computer, selects oneof said plurality of partitions corresponding to the SCSI-ID receivedfrom the host computer, and controls access to the selected partition inaccordance with the SCSI command received from the host computer.
 6. Adisk array storage device according to claim 5, wherein the SCSI commandincludes a Logical Unit Number.
 7. A disk array storage device,comprising:a disk array divided into a plurality of subgroups, eachassigned a different Small Computer System Interface (SCSI) ID; and adisk array controller connectable to a host computer via an SCSI bus andto said disk array; wherein said disk array controller receives anSCSI-ID from the host computer via said SCSI bus, recognizes if thereceived SCSI-ID coincides with any of the SCSI-IDs assigned to saidplurality of subgroups, responds to the host computer if coincidence isrecognized, receives an SCSI command from the host computer, selects oneof said plurality of subgroups corresponding to the SCSI-ID receivedfrom the host computer, and controls access to the selected subgroup inaccordance with the SCSI command received from the host computer.
 8. Adisk array storage device according to claim 7, wherein the SCSI commandincludes a Logical Unit Number.
 9. A disk array storage device accordingto claim 7, wherein each of said subgroups includes portions of multipledisks of said disk array.
 10. A disk array storage device according toclaim 9, wherein each of said subgroups is assigned one of RAID levels.11. A disk array storage device, comprising:a disk array divided into aplurality of storage areas, each assigned a different Small ComputerSystem Interface (SCSI) ID; and a disk array controller connectable to ahost computer via an SCSI bus and to said disk array; wherein said diskarray controller receives an SCSI-ID from the host computer via saidSCSI bus, recognizes if the received SCSI-ID coincides with any of theSCSI-IDs assigned to the storage areas, responds to the host computer ifcoincidence is recognized, receives an SCSI command from the hostcomputer, selects one of said plurality of storage areas correspondingto the SCSI-ID received from the host computer, and controls access tothe selected storage area in accordance with the SCSI command receivedfrom the host computer.
 12. A disk array storage device according toclaim 11, wherein the SCSI command includes a Logical Unit Number.
 13. Adisk array storage device, comprising:a disk array divided into aplurality of devices, each assigned a different Small Computer SystemInterface (SCSI) ID; and a disk array controller connectable to a hostcomputer via an SCSI bus and to said disk array; wherein said disk arraycontroller receives an SCSI-ID from the host computer via said SCSI bus,recognizes if the received SCSI-ID coincides with any of the SCSI-IDsassigned to the devices, responds to the host computer if coincidence isrecognized, receives an SCSI command from the host computer, selects oneof said devices corresponding to the SCSI-ID received from the hostcomputer, and controls access to the selected device in accordance withthe SCSI command received from the host computer.
 14. A disk arraystorage device according to claim 13, wherein the SCSI command includesa Logical Unit Number.